This invention relates in general to catalytic combustion processes, e.g. for use in water tube boiler applications.
The use of catalysts in the place of conventional burners for promoting hydrocarbon oxidation reaction provides advantages in the control of emissions. Most catalytic combustors of conventional design operate at near-adiabatic conditions. Stoichiometric operation of these conventional catalytic combustors is precluded by the combustor material because the temperature limits of these materials must be maintained far below the stoichiometric flame temperature. The result is that operation of conventional off-stoichiometric catalytic combustors can result in inefficient systems. If the system employs a single stage combustor, then to keep the flame temperature down to acceptable levels air or fuel, or both, must be added. Where a multiple stage combustor is operated with fuel-rich combustion at a lower temperature in the first stage then secondary air must be added for the next combustion stage. In a Flue Gas Recirculation (FGR) System a portion of the exhaust stream is recirculated into the combustor for purposes of increasing system efficiency.